Field of the Invention:
The present invention relates generally to check valves and, more specifically, to check valves with a spring return mechanism. Still more specifically, the present invention relates to check valves having a resilient disc in combination with a spring return mechanism.
Check valves having a closure mechanism consisting of a resilient disc have been commonly used in water and wastewater systems to prevent reverse flow in such systems. Typically, these resilient disc check valves have a disc that is mounted within the valve body at a 45 degree angle with respect to the flow path when in a closed position. The disc includes a hinge which is typically integrally molded to the disc and is rigidly held in place in the valve body. The resilient disc typically pivots about 35 degrees to an open position thereby providing a full flow area or near full flow area. The 35 degree span of movement is preferred because it provides a short closing stroke which avoids a slamming of the valve in a closed position. The above-described design is reliable because there is only one moving part--the resilient disc. Further, the integral connection between the hinge and the disc avoids any penetrations of the disc for a connection between the hinge and the disc.
While the standard resilient disc check valve design is reliable and economical, many applications demand the incorporation of a spring return element. Spring return elements are desirable because they prevent the occurrence of valve slam and water hammer by biasing the disc into the closed position before the flow reverses in the pipe. In contrast, if the flow reverses in the pipe before the disc is in the fully closed position, the reverse flow will slam the disc into the seat and violent forces within the pipe and noise will result. The sudden stoppage of the reverse flow can also cause the phenomenon known as water hammer in the pipe. Accordingly, to avoid these problems, spring return mechanisms are often provided with resilient disc check valves. However, the currently-available spring return mechanisms include components that are external to the valve body and are also costly to fabricate.
Specifically, one currently-available spring return mechanism is sold under the APCO trademark by the Valve and Primer Corporation of Schaumburg, Ill. However, the design of this valve requires the valve body to be penetrated as the spring mechanism passes through the valve body and is contained within a spring housing that is mounted onto the top of the valve body. The penetration of the valve body in order to accommodate the spring mechanism reduces the reliability of the valve and increases the cost of manufacture. Further, because the spring mechanism is attached to the disc with fasteners that penetrate the disc, the disc is susceptible to leakage as well as a loss of integrity of the bonding material disposed on the upstream side of the disc which can lead to subsequent corrosion and failure of the valve. Further, the spring mechanism extends across the flow path of the valve body and is susceptible to catching debris in wastewater applications. A build up of such debris on the spring mechanism can prevent full rotation of the disc and thereby interfere with the operation of the valve.
Another type of commonly employed spring return mechanism for disc valves is sold by Dresser Manufacturing Division of Dresser Industries, Inc. of Anniston, Ala. One disadvantage of this type of spring mechanism is that the spring is mounted exterior to the valve. The spring biases the disc to a closed position via a lever and hinge pin connection. This type of external mechanism cannot be employed with a resilient disc because resilient discs require the hinge to remain stationary as the disc moves towards the open or closed position. Thus, in addition to requiring moving parts disposed outside of the valve body, which is ultimately unreliable and more costly, the afore noted design is not suitable for resilient disc check valves.
Therefore, there is a need for an improved spring return mechanism for resilient disc valves which will not require rotational or pivotal movement of the hinge or hinge pin and which will not require penetration of the valve body or the addition of any special type of housing on the valve body to accommodate the spring mechanism. Further, there is a need for a spring return mechanism for a resilient disc check valve which does not extend across the flow path and which therefore would not be susceptible to catching or retaining debris if used in wastewater applications. Further, there is a need for a spring return mechanism for a resilient disc valve that does not require a fastener or other means of attaching the spring element to the disc which requires penetration of the disc.